The present invention relates to a system and method for positioning a medical instrument and/or directing a medical procedure within a patient's body. More particularly, the present invention relates to an internal power source free transponder, transplantable within the body, which, in response to a positioning field signal, relays a locating signal outside the body, thereby enabling the precise localization of the transponder within the patient's body.
Various medical procedures require precise localization of the three-dimensional position of a specific intra body region in order to effect optimized treatment.
For example, localization and sampling of a suspected tumor is effected in breast biopsy procedures, by typically using a system known as a core biopsy system. The core biopsy system first obtains a stereo-mammogram from a patient's breast, while the breast is immobilized by being compressed between two plates. The stereo-mammogram is used to calculate the three dimensional (3D) coordinates of the suspected tumor. A needle is then fired into the breast and a biopsy of the suspected tumor is aspirated. If the biopsy is positive, the patient is scheduled for a tumor removal surgery. It should be noted that before the biopsy procedure is commenced, the tumor needs to be manually identified by a physician.
Following biopsy of the tumor the surgical procedure, if necessary, generally proceeds in the following manner. The patient undergoes multi-plane mammography, a radiologist examines the film, and then inserts a wire into the breast so that it punctures the tumor. This procedure is visualized using repetitive x-ray imaging or preferably stereotactic breast imaging systems which can localize the tumor more precisely and assist in the insertion of the wire. The surgeon then cuts the breast open, following the wire until the tumor is found and excised.
Although utilizing the core biopsy system along with surgery is currently the method of choice when dealing with breast cancers and various other cancers, such a method suffers from several crucial limitations.
Since there is large difference between the position and shape of the breast during mammography and surgery, images taken during mammography are unusable for stereotactic positioning during the surgical procedure, thus greatly complicating and prolonging the tumor removal procedure and leading to undue discomfort to the patient.
In addition, serious limitations of the above mentioned procedure result from the implantation of a long wire often present in the breast for many hours at a time while the patient awaits surgery. The surgeon must follow this wire into the breast to the located tumor, although ideally, the entry pathway into the breast should be designed independently of the wire, since this implanted wire may not always represent the optimal entrance trajectory. In addition, the presence of wire(s) extending outside the breast greatly increases the risk of infection. Another example of a medical procedure which benefits from tissue region localization is minimally invasive surgery. Although minimally invasive surgery is currently limited in the applications thereof, it presents numerous benefits over conventional surgery. In comparison to conventional surgical methods, minimally invasive surgery reduces the time and trauma of surgery, postoperative pain and recovery time, making the surgical procedure safer and less discomforting to the patient. Examples of medical instruments developed for minimally invasive surgery include laparoscopic, thoracoscopic, endoluminal, perivisceral endoscopic, and intra-articular joint instruments.
Minimally invasive surgery can also use a variety of radiation sources such as lasers, microwaves, and various types of ionizing radiation, to effect tissue manipulation. In addition, cryosurgery has also been used in a minimally invasive manner to treat carcinoma of the prostate, breast, colon and other organs.
A major hurdle facing the surgeon or radiologist in using minimally invasive surgical instruments has been the difficulty in visualizing and positioning such instruments. Decreasing instrument size and increasing complexity of operations have placed greater demands on the surgeon to accurately identify the position of the instruments and the details of the surrounding tissue. Visualization is a critical component to the successful use of minimally invasive surgical or diagnostic instruments.
In laparoscopic surgery, for example, visualization is accomplished by using fiber optics. A bundle of microfilament plastic fibers is incorporated in the instrument and displays a visible image of the field of interest to the surgeon. The quality of this image directly impacts the surgeons ability to successfully manipulate tissue within the patient's body.
Still another area which can benefit from intrabody localization and positioning of tissue regions is robotic assisted surgery. Recent advances in medical imaging technology, such as, for example, magnetic resonance imaging (MRI), especially open-MRI, and computer tomography (CT), coupled with advances in computer-based image processing and modeling capabilities have given physicians the ability to visualize anatomical structures in patient's, in real time, and to use this information in diagnosis and treatment planning.
The precision of image-based pre-surgical planning often greatly exceeds the precision of actual surgical execution. Precise surgical execution has been limited to procedures, such as brain biopsies, in which a suitable stereotactic positioning frame is available. The restricted applicability of such a frame or device has led many researchers to explore the use of robotic devices to augment a surgeon's ability to perform geometrically precise tasks planned from computed tomography (CT) or other available image data. Machines are very precise and untiring and can be equipped with any number of sensory feedback devices. Numerically controlled robots can move a surgical instrument through a defined trajectory with precisely controlled forces. On the other hand, a surgeon is very dexterous, and is highly trained to exploit a variety of tactile and visual information. Although combining the skills of a surgeon with a robotic device can substantially increase the effectiveness and precision of various surgical procedures, such a robotic surgical device must have a precisely defined frame of reference, such as body coordinates, without which it cannot operate with precision.
Yet another type of medical procedure which can greatly benefit from intrabody localization and positioning of tissue regions involves non invasive radiation treatment of tumors, thrombi, vascular occlusions, enlarged prostate, and other physiological disorders.
Examples of such procedures include, but are not limited to, the irradiation of cancerous or benign tumors by a high intensity radioactive source or particle accelerator, the "gamma knife", which employs a highly focused gamma ray radiation obtained from crossing or collimating several gamma radiation beams, the ablation of the prostate by microwave heating, the necrosis of diseased cells following ultrasonic radiation treatment, and local ultrasonically induced drug activation. With all of these applications it is critical that the focus of the energy be precisely directed to the area to be treated, otherwise unwanted damage is inflicted upon the healthy surrounding tissue.
To enable the precise localization of the instruments or radiation beams of the above mentioned procedures, stereotactic positioning is typically employed. This method maps the outer surface of a body, or any part, which is held immobile. Positioning can also employ sensors such as, for example, magnetic sensors (see, for example, U.S. Pat. No. 5,558,091) or acoustic transducers, which are positionably fixed to the skin. In yet another approach, light emitting beacons positioned on the skin, and whose position is measured externally by an appropriate imaging system are used (see, for example, U.S. Pat. No. 5,279,309). The spatial positioning of internal bodily organs is then determined relative to this stereotactic frame using conventional imaging system, such as MRI, CT or ultrasound.
As practiced today, the stereotactic approach is primarily used in intracranial surgical procedures, since the skull provides a convenient and rigid stereotactic frame.
Although using extracorporeal referencing devices and methods is advantageous for being non invasive, such positioning means are limited by the fact that the position of intrabody regions of interest constantly change, either due to deformation of elastic structures (e.g., the breast, organs inside the abdominal cavity) or due to the progression of the disease (e.g., intracranial swelling). Thus, stereotactic methods cannot be used for precise and automated medical procedures, especially those relating to soft tissue.
An alternative procedure is disclosed in U.S. Pat. No. 5,868,673 which describes a spatial tracking and imaging system for obtaining an accurate position of a medical instrument as it is maneuvered by an operator, and to mark a location on the subject bodily structure. The spatial positioning is effected by implanting reference transducers at the desired location in the body, which are connected by thin wires to connection pads or electronic circuits placed externally to the body. The transducers can receive and/or transmit ultrasonic energy, and as such signal their position relative to a set of mobile transducers placed at known locations on the body at the time of the procedure. The mobile and reference transducers communicate by sending ultrasonic impulses in either direction, which yields the relative position of the reference transducers. Alternatively, the mobile transducer may be placed at the tip of a surgical device, and as such employed to guide the tip in relation to the reference transducers.
This system suffers from several limitations resultant from the extracorporeal wire connection of the implanted reference transducer. The use of such wires prevents the use of this design in intracranial applications, such as, for example, intracranial surgery. Further still, externally provided wires traversing the body into deep internal organs serve as potential conduits for infection. A further limitation of this design is that wired devices cannot be left inside the body, but instead, have to be removed within a relatively short time following the procedure. The removal procedure, which may necessitate full surgery, can be more traumatic to the patient than the insertion. In addition, since discomfort to the patient is wantedly minimized, such wires have to be thin, and as such fragile, and can break during the surgical procedure. Such a sudden loss of positioning information in the course of a surgical procedure can lead to catastrophic results.
In addition to the limitations imposed by the wiring of the reference transducer, a further disadvantage of the above mentioned method is that it yields only positions relative to external reference points provided by the reference transducers which are placed in contact with the patient's skin. In applications which involve radiation that emerges from fixed sources (e.g., the collimated gamma radiation beams used in a "gamma knife"), it would be advantageous to have spatial positioning information relative to the radiation source. Such information cannot be provided by the system disclosed in U.S. Pat. No. 5,868,673.
Finally, the above mentioned system depends on the transmission of acoustic signals to obtain the positioning information, using either time-of-flight or phase information. Such a system is rendered unusable in some surgical procedures. During surgery various air gaps are opened in the body, caused by small openings opened in minimally invasive procedures, inflating the abdominal cavity with carbon dioxide during some laparoscopic procedures, or full open surgery. Such air gaps either cut off ultrasonic communication between the reference and mobile transducers, or change the intra-body acoustic propagation conditions so that precise positioning information is hard to obtain.
Another position localization approach comprises the implantation of fiducial markers at various positions within the body (see, for example, U.S. Pat. Nos. 4,945,914; 4,991,579; 5,394,457; and 5,397,329). In these systems and methods, the implants comprise a passive structure which is limited in properties to a specific imaging system. Typically, and as disclosed in the above referenced patents, fiducial markers include contrast materials for MRI, X-ray fluoroscopy or CT scanners and ultrasound. The imaging data is scanned for the presence and position of such markers, and these positions, when processed through a dedicated algorithm, form the anchor points for the spatial positioning reference frame.
Systems and methods incorporating fiducial markers are advantageous in being standalone implantable devices, which do not require external connections. However, each marker type can only be used with a specific imaging system, which greatly limits the application of such markers. In addition, when utilizing X-ray fluoroscopy or CT markers, the imaging process necessitates exposure to ionizing radiation. Furthermore, MRI and CT systems are bulky, intrusive and complicated to operate. Finally, ultrasonic imaging systems, for the most part, do not yield independent 3D positions, and suffer from the disadvantages detailed above.
Yet another positioning method is disclosed in U.S. Pat. No. 5,161,536 which describes the implantation of an actual active transponder inside the body. This transponder actively returns ultrasonic pulses sent by a probe of a conventional ultrasonic imaging system. The returning pulse is picked up, synchronized and analyzed by the imaging system to yield the position of the implant superimposed on the ultrasound image. This ensures a good signal-to-noise ratio, ease of operation, and also avoids the ambiguities associated with transmission sidelobes. However, it does share most of the disadvantages of other fiducial marker methods. In addition, it requires an independent power source, such as a battery, which limits its lifespan and increases the size of such a transponder.
Thus, a limitation common to all of the above mentioned positioning systems and methods is the lack of precise, telemetric, spatial localization of intrabody regions provided as information which is usable as machine input.
There is thus a widely recognized need for, and it would be highly advantageous to have, a system and method for positioning a medical instrument and/or directing a medical procedure within a patient's body devoid of the above limitation.